The effect of repeated stress or prolonged CORT treatment on glutamatergic responses and GluR1/NR1 expression is blocked by the specific inhibitors Selleck Tenofovir of proteasomes, but not lysosomes. It suggests that GR-induced ubiquitination of GluR1 and NR1 subunits tags them for

degradation by proteasomes in the cytoplasm, therefore fewer heteromeric AMPARs and NMDARs channels are assembled and delivered to the synaptic membrane. Interestingly, infusion of a proteasome inhibitor into PFC prevents the loss of recognition memory in stressed animals, providing a potential approach to block the detrimental effects of repeated stress. To further understand the mechanisms underlying the specific ubiquitination of GluR1 and NR1 in PFC by repeated stress, we have explored the potentially participating E3 ubiquitin ligase, which determines selectivity for ubiquitination by bridging target proteins to E2 ubiquitin-conjugating enzyme and ubiquitin. NR1 subunits are found to be ubiquitinated by the E3 ligase Fbx2 in the ER (Kato et al., 2005), a process affecting PARP inhibitor the assembly and surface expression of NMDARs. Studies in C. elegans also indicate that GLR-1 is ubiquitinated in vivo, which regulates the GLR-1 abundance at synapses ( Burbea et al., 2002, Juo and Kaplan, 2004 and Park et al., 2009). Moreover,

the E3 ligase Nedd4-1 has been recently shown to mediate the agonist-induced GluR1 ubiquitination in neuronal cultures, which affects AMPAR endocytosis and lysosomal trafficking ( Schwarz et al., all 2010 and Lin et al., 2011). Using RNA interference-mediated knockdown in vitro and in vivo, we demonstrate that the suppression of AMPAR and NMDAR responses induced by long-term CORT treatment or repeated stress requires Nedd4-1 and Fbx2, respectively. Moreover, Nedd4-1 is required for the increased GluR1 ubiquitination and Fbx2

is required for the increased NR1 ubiquitination in repeatedly stressed animals. Both E3 ligases are also required for the stress-induced impairment of cognitive processes. The higher expression level of these E3 ubiquitin ligases in PFC than other brain regions, along with the upregulation of Nedd4-1 in PFC from stressed animals, potentially underlies the selective increase of GluR1 and NR1 ubiquitination and degradation in PFC neurons after repeated stress. Future studies will further examine the biochemical signaling cascades underlying the GR-induced changes in the activity and/or expression of Nedd4-1 and Fbx2. Taken together, this study indicates that in response to repeated stress, the key AMPAR and NMDAR subunits, GluR1 and NR1, are degraded by the ubiquitin-proteasome pathway in PFC neurons, causing the loss of glutamate receptor expression and function, which leads to the deficit of PFC-mediated cognitive processes.